1. Field of the Invention
The present invention generally relates to injection molding machines having accumulators and control methods for the injection molding machine. More particularly, the present invention relates to an injection molding machine having an accumulator supplying oil to an actuator so that the actuator is actuated and a control method for the injection molding machine.
2. Description of the Related Art
A related art injection molding machine includes an injection apparatus and a mold clamping apparatus. In the related art injection molding machine, a screw is disposed inside a heating cylinder so that the screw can be rotated about an axis and can be advanced and retracted. In a metering process, the screw is rotated so that a resin supplied from the hopper to the heating cylinder is heated, melted and advanced. Because of this, a front part of the screw head formed at a front end of the screw is filled with the resin.
In an injection process, the screw is advanced so that the resin in the front part of the screw head is injected from an injection nozzle. As a result of this, a cavity space of the mold clamping apparatus is filled with the resin. A pressure of the resin in the cavity space of the mold clamping apparatus is held in a holding pressure process. After that, in a cooling process, the resin is cooled so that a molded article is obtained.
In such the related art injection molding machine, a screw motor that is a hydraulic motor is provided for rotating the screw. In addition, an injection cylinder is provided for advancing the screw.
Furthermore, a hydraulic circuit is formed at the injection molding machine. That is, in the hydraulic circuit, oil transmitted from a hydraulic pump is supplied to the hydraulic motor and the injection molding cylinder by an accumulator, so that the hydraulic motor and the injection molding cylinder are driven. That is, the accumulator functions so as to supply a sufficient amount of the oil to the hydraulic motor and the injection molding cylinder and hold a designated pressure in the hydraulic circuit.
Accordingly, the oil having a designated pressure (hereinafter an “accumulator pressure”) is accumulated in the accumulator. In addition, in the injection process and the holding pressure process, the oil that is accumulated in the accumulator and has the designated pressure is supplied to the injection cylinder by a valve for adjusting the flow amount and the pressure, so that the velocity of the screw and the force for holding pressure are controlled.
However, in the related art injection molding machine having the above mentioned hydraulic control system, in a case where the accumulator pressure is much higher than the pressure generated by the oil that is supplied to the injection cylinder during the injection process, oil causing the unnecessarily high accumulator pressure is accumulated in the accumulator. This causes a useless consumption of energy so that it is difficult to produce the molded article with good energy efficiency.